1. Field of the Invention
This invention relates to the detection of nuclear radiation by means of a synthetic diamond detector.
2. Discussion of the Prior Art
The detection of nuclear radiation using diamond detectors per se is well known. According to the literature, it is necessary for diamonds to have very low impurity concentrations in order to be suitable for this application. In the case of synthetic diamonds, it has been proposed that a nitrogen impurity concentration of less than 20 parts per million (ppm) is necessary for use in nuclear radiation detectors--see for example, in European Patent Publication Number 0052397 (Burgemeister).
Diamond is composed of the single element carbon and, to date, only nitrogen and boron are known with certainty to be incorporated into the diamond lattice. Nitrogen atoms may be bonded into the diamond as:
(a) a single nitrogen atom replacing a carbon atom. This form of nitrogen is known as the single substitutional nitrogen;
(b) a pair of adjacent nitrogen atoms (called an A-aggregate) replacing a pair of carbon atoms; or
(c) a cluster of nitrogen atoms referred to as the B-aggregate or B form of nitrogen. The exact molecular form of this nitrogen is still unknown. It would appear from the experimental data available that the cluster involves four nitrogen atoms.
Each of the above mentioned forms of bonded nitrogen atoms displays characteristic infrared and ultraviolet absorption spectra which are signatures of their presence. It should be pointed out that such spectra by themselves do not provide quantitative concentrations of the type of nitrogen impurities present.
According to the Robertson, Martin and Fox scale, diamonds are typified by the presence and concentration of the nitrogen within the diamond: